This invention involves a temporary manhole cover and method of using the cover to protect the manhole entrance as required.
The standard manhole is about two feet in diameter and provides access to underground systems such as sanitary sewer systems and utility lines. In essentially all of these systems, water and weather intrusion into the underground system is to be avoided. The standard manhole cover is a circular cast iron solid disk over one inch thick and designed to be removed only by authorized personnel using tools designed to provided sufficient leverage from above.
Once the cast iron cover, weighing almost 175 pounds, has been lifted and slid off to a side of the manhole, a work person can climb down the manhole. Because of safety requirements, it is necessary to provide a fence around the open hole and appropriate flashing lights and the like to prevent persons from falling into the hole or driving a car over and dropping into the opening. It is further necessary to station a second person above the hole, again for safety purposes. Despite these precautions, the open hole still presents a substantial safety hazard. Not only do unauthorized persons ignore or avoid the barrier, but cars sometimes hit the barrier and end up with a wheel wedged into the manhole. Further, the open hole presents substantial risk to the person working below due to falling objects that inadvertently fall into the manhole. In cases of severe emergency or when multiple manholes must be open at the same time, there may be insufficient personnel. A person working alone at a manhole or when a number of persons are needed down the manhole, the present system is insufficient.
It is important to distinguish between manhole covers and drain grates. Cast iron grates are interfitting into a hole which routinely opens to storm drainage systems below ground. The purpose for these grates is to allow water to flow into the system while preventing intrusion of large foreign objects from above. These systems, by their very nature, are essentially never closed. Grates or catch basin covers are designed and constructed so that it is essentially impossible to lift them out without a leveraging tool. A grate is described in U.S. Pat. No. 4,345,998 to Graffis, et al, the grate being constructed of polyethylene plastic or other "structural plastic materials". A catch basin interceptor covered by a support grill is disclosed in U.S. Pat. No. 4,136,010 to Pilie', et al. A modular trench drain system covered by a linear grate panel is described in U.S. Pat. No. 5,066,165 to Wofford, et al. A rectangular drain grate constructed of glass filled polypropylene is disclosed in U.S. Pat. No. 5,130,016 to Gavin. A solid manhole cover constructed of a polyethylene polymer skin filled with cured cement is disclosed in U.S. Pat. No. 5,123,776 to Lang, et al. A rectangular grate is disclosed in French Patent No. 79 12029, Publication No. 2,456,169 to Morel. With only the abstract available, the composition of the grate is cross-hatched for plastic. A manhole closure in the form of a barrier pan constructed of any suitable impervious, non-corrosive material such as plastic, fiberglass or stainless steel is disclosed in U.S. Pat. No. 4,512,492 to Graybeal. The prior closure is impervious except for a two-way gas pressure release value. A water sealed system of a manhole rim and cover assembly is a described in U.S. Pat. No. 5,201,151 to LeBlanc, et al. A solid access cover assembly constructed of composite plastic material and steel is described in U.S. Pat. No. 5,312,202 to Newton. A ramp with a center hole for a temporarily elevated utility access hole constructed of an elastomeric material is disclosed in U.S. Pat. No. 5,308,188 to Shaftner.
None of these devices and methods of use satisfy the above needs nor attain the objects described herein below.